1. A thoroughly unprincipled person; a scoundrel.
2. A foul-mouthed person.
3. The criminals and vagrants or vagabonds of a town or community, collectively.
4. A person of stained or low character, esp. one who uses scurrilous language, or treats others with foul abuse; a scoundrel; a rogue.
5. A vagrant; a bootblack; a gamin.
6. A guy who runs EQII.com

A man whose manners and sentiments are decidedly below those of his class deserves to be called a blackguard.

A blackguard is a knight that serve opposite of a paladin. Blackguards go about with corrupting, sneaking, committing treachery, and straightforward smiting of good. They are often called Antipaladins because of their wholly evil nature. They often wear black armors with lots of nice bloodstains.

Steve was the blackguard of the group, he loved nothing more than to rip the heads off of those lousy dogooders.